This invention relates to the structure of an automatic transmission for assuring the lubrication of a one-way brake within the automatic transmission.
FIG. 10 illustrates the mounting structure of a one-way brake in accordance with the prior art. A clutch C2, a first brake B1, a planetary gear unit 7 and a second brake B2 are arranged in the order mentioned, starting from the engine output side, about an input shaft 1 of an automatic transmission mechanism. A hollow shaft 8 is freely rotatably fitted on the input shaft 1. The planetary gear unit 7 is of the dual type and includes a sun gear S formed on the hollow shaft 8, and a carrier CR supporting a pinion P1 meshing with the ring gear R2.
The clutch C2 is interposed between a sun gear input flange 9, which is fitted on the hollow shaft 8, and a hub 10 fitted on the input shaft 1, and is engaged and disengaged by a piston 12 within a clutch cylinder 11. A brake drum 13 is arranged about the clutch cylinder 11. The first brake B1, which comprises a band brake, is arranged so as to contact and separate from the drum 13.
A counterdrive gear 14 is arranged between the clutch C2 and the planetary gear unit 7. The drive gear 14 is splined at its inner periphery to the carrier CR and has an outer periphery freely rotatably supported via a bearing 16 on a bearing outer race 50 attached to a transaxle case 2. The bearing outer race 50 is splined to a cylinder portion 51 of the transaxle case 2 and to an inner race 52 of a one-way brake F. Rotation of the one-way brake F is stopped by the cylinder portion 51 via the splines. In the axial direction of the bearing outer race 50, the right end is fixed by the end face of the cylinder portion 51, and movement in the leftward direction is prevented by a snap ring 53. The one-way brake F has an outer race 54 welded to the ring gear R2 of the planetary gear unit 7, and the second brake B2, which is of disc-type, is interposed between the outer periphery of the ring gear R2 and the axle case 2. The brake B2 is engaged and released by a piston 17.
In this conventional automatic transmission, the one-way brake F is lubricated as follows. Oil which has been dispersed from the input shaft 1 from the inner side of the inner race 52 on the inner peripheral side of the brake F descends under the force of gravity and is scraped up and collected for lubrication. The oil is also forcibly supplied from the transaxle case 2.
However, in the above arrangement wherein the one-way brake is fixed on its inner peripheral side, the inflow of the lubricating oil is unsatisfactory. In particular, the amount of lubrication is insufficient in an arrangement where only the force of gravity is relied upon to cause the oil to descend. This makes it necessary to increase the amount of lubricating oil supplied, as a result of which the discharge capacity of the oil pump must be increased. Furthermore, since the one-way brake is locked only in first speed and in reverse and is released in other speed ratios, the brake is often in a slipping state. When the outer peripheral side is rotated at high speed in such case, the lubricating oil is scattered to the outside by centrifugal force, thereby inviting insufficient lubrication. If rotation of the outer peripheral side continues for an extended period of time, there is an increase in the amount of heat produced by the sliding of the lubricated portions. If the amount of lubricating oil is inadequate at such time, the cooling effect is unsatisfactory and, hence, the sliding portions of the one-way brake tend to burn out.
In the arrangement where the oil is forcibly supplied from the transaxle case 2, sealing members and the machining of oil supply holes are required. Moreover, in order to prevent leakage of oil to other components, bushes and seal rings are required. The result of these requirements is higher cost.